Keeping Spider Mites Away
Plant your tomato plants where they stay warm without drying out. Tomato plants need at least 7 hours of sunlight every day to grow successfully. Plant your tomatoes outside in a location that gets enough sunlight, but isn’t in the direct path of the afternoon sun. Tomato plants that are in the perfect environment, with sufficient sunlight and moisture, will be much less likely to develop a spider mite infestation. Also consider planting your tomatoes in a location where they can take advantage of radiant heat, such as next to large boulders or a building. If planting your tomatoes in a pot, take advantage of the fact that you can move those pots if required. Move the pots into the morning sun each day, then move them out of the direct afternoon sun to prevent them from drying out.
Ensure your tomato plants are growing in loamy soil with lots of organic matter. In general, tomato plants aren’t overly fussy when it comes to the soil, however, the proper soil conditions will help ensure the soil stays moist and will not create conditions where spider mites may thrive. Plant your tomato plants in soil that is loamy, with lots of organic matter (compost, peat moss, or manure). The pH level of the soil for tomato plants should be between 6.0 and 7.0. If you’re planting your tomatoes in pots, use high-quality vegetable potting soil to preserve soil moisture. Also, use vegetable fertilizer in your pots to provide your tomato plants with sufficient nutrients.
Place hot pepper or garlic in the soil to prevent spider mites. Spider mites are not fans of hot peppers or garlic. When planting your tomatoes (either in your garden or in a pot/container), spray the soil under the plants with homemade hot pepper or garlic spray to keep spider mites away and prevent them from harming your tomato plants. For the hot pepper spray, add 1 teaspoon (4.9 mL) of cayenne pepper flakes to 1 cup (240 mL) of water in a spray bottle. Shake the bottle to mix the ingredients and allow them to sit for at least 24 hours before using it. For the garlic spray, add 2 mashed garlic cloves to 1 litre (4.2 c) of water in a bowl or jug. Allow the mixture to sit for 24 hours and then strain out the garlic pieces. Put the mixture into a spray bottle to use.
Apply diatomaceous earth to the soil around your tomato plants. Purchase food-grade diatomaceous earth (D.E.) from a garden centre, hardware store, or online. Sprinkle the D.E. on the soil, in unbroken rings, around your tomato plants. You can also sprinkle or dust the D.E. directly onto the leaves of your tomato plants. Spider mites will not attempt to cross the D.E. barrier around the plants, but you do need to reapply D.E. after it’s rained or you’ve soaked the plants. D.E. is the powdered fossilized skeletons of microscopic organisms called diatoms. It is a mined substance that is found in areas where lakes were present millions of years ago. Do not apply any D.E. to the flowers on your tomato plants. D.E. doesn’t distinguish between good and bad insects and may harm pollinators if applied to the tomato plant flowers.
Move your tomato plants indoors to protect them if you can. If you’ve planted your tomatoes in pots, you can move them indoors for a variety of reasons. First, it will be easier to control the humidity around your plants when they’re indoors. Second, having your tomato plants indoors may help you prevent and/or control spider mites. If only some of your tomato plants are infested with spider mites, keep them outside and move the uninfested plants indoors to protect them. If all of your tomato plants are infested with spider mites, spray down the plants with a hose before moving them inside. Once indoors, keep the tomato plants away from any other plants you may have.
Deterring Mites with Moisture
Use black mulch to preserve soil moisture for your tomatoes. Once planted, apply a layer of black mulch (3 to 6 inches (7.6 to 15.2 cm)) on top of the soil around your tomato plants. You can add mulch to both gardens and pots. The mulch will keep the soil moist, but will also help control weeds and prevent ground rot. You can use commercial mulch that comes in plastic bags from a garden centre, or you can use straw. When laying the mulch on the ground, keep a 1 in (2.5 cm) space around the stem of your tomato plants to prevent fungal problems.
Soak your tomato plants every 7-10 days to prevent rot. Watering your tomato plants frequently and lightly can cause tomatoes to crack or the blossoms of the plants to rot. It can also allow the development of foliage disease. Soak the soil around your tomato plants every 7 to 10 days instead. When soaking your tomatoes, spray the undersides of the leaves with your hose to remove any initial spider mites that may have started to make a home. If the soil around your tomato plants is drying out before your next watering day, increase the frequency of the soaking. Tomatoes planted in pots may need to be soaked more frequently, as pots tend to dry out faster.
Use a hose to remove spider mites from your plants. The spray from an outdoor hose is of a high enough pressure to help keep spider mites from being able to make a home on your tomato plants. Spray your tomato plants with a hose, especially on the undersides of the leaves, on a weekly basis. This spray will help keep spider mites away and will also water your tomato plants. This method can be used on tomatoes planted in a garden and planted in pots. Be careful that the spray of water isn’t too strong that it damages the tomato plants. You may want to use the nozzle and spray upwards on the plants to get the undersides of the leaves. Or, hold the leaves with your hands and turn them over before spraying them.
Keep a layer of water in your pot saucers to increase soil moisture. Spider mites hate moist conditions. To help prevent spider mites on your tomato plants, ensure there is always a layer of water in the tray or saucers in which your tomato pots or containers are sitting. This water will keep the soil moist, which in turn, should help keep spider mites away. This method will only work for tomato plants in pots. However, if you put your tomato plants in a garden, you can leave buckets or pots of water in and around your plants to increase the general moisture around your tomatoes. This is especially important when the conditions are hot and dry. Tomato plants that are water-stressed are more susceptible to spider mite infestations.
Install a humidifier close to your tomato plants to increase the moisture level. Cluster your potted tomatoes together on a porch or deck and place a humidifier in the middle of the cluster. Keep the humidifier going during the driest parts of the day. If your tomato plants are indoors, put the humidifier anywhere in the same room as the plants. Remember to check the reservoir of the humidifier frequently and keep it full of water.
Controlling an Infestation
Cut off and remove parts of your tomato plants that are infested. Once an infestation has progressed, you may need to resort to more drastic measures. If you notice specific parts of your tomato plants appear bleached or bronzed, or if the leaves have started to curl, cut those pieces off using garden shears. Dispose of the infected portions of your tomato plants in the garbage or by burning them. Do not put them in your compost pile or you may spread the infestation to other plants in the future.
Spray insecticidal soap on tomato plants to kill spider mites. Purchase a commercially-made insecticidal soap at a garden centre or hardware store or make your own. Spray the soap onto your tomato plants, making sure to focus the spray on the undersides of the leaves where spider mites live. Reapply the soap again if you see continuing evidence of spider mites on your tomato plants. Make your own insecticidal soap by combining 1 teaspoon (4.9 mL) of mild liquid soap (such as castile soap) to 1 litre (4.2 c) of lukewarm (slightly warm) water in a spray bottle. Shake the spray bottle before using the soap. Do not use insecticidal soap on tomato plants that are water-stressed or when the temperatures are higher than 90 °F (32 °C).
Apply horticultural oil to your tomato plants to eliminate spider mites. Some highly refined oils are considered superior or horticultural oils. Spray the oil directly onto your tomato plants, especially on the undersides of leaves. The oil will essentially drown the spider mites without damaging the tomato plant. Make sure you read the manufacturer’s instructions before using the oil. Superior or horticultural oils are non-toxic, which means they will impact bad insects (like spider mites), but should not impact beneficial insects (like those that eat spider mites). These oils are designed not to harm the plant itself if used properly. It is important to read the manufacturer’s instructions to ensure you do not damage your tomato plants. Do not use superior or horticultural oils on tomato plants that are water-stressed or when the temperatures are higher than 90 °F (32 °C).
Use neem oil to control and prevent spider mites. Purchase concentrated neem oil from a garden centre, hardware store, or online. Combine 1.5 teaspoons (7.4 mL) of neem oil concentrate to 1 teaspoon (4.9 mL) of mild liquid soap (such as castile soap) and 1 litre (4.2 c) of lukewarm (slightly warm) water in a spray bottle. Shake the bottle to mix the ingredients and spray directly onto your tomato plants, specifically on the undersides of the leaves. Neem oil spray can take a while to work on spider mites. To give it the best chance to work properly, wipe off the leaves (with a sponge or cloth) of your tomato plant first to remove as many spider mites as possible. Neem oil spray can also be used as a preventative measure if sprayed on tomato plants regularly once leaves have formed.
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